With the progress of information-oriented society, techniques for the security protection of information processing systems have advanced. For example, ID cards have been used for entrance control for a computer room. However, there is a high chance that an ID card will be lost or stolen. For this reason, an individual recognition system has begun to be introduced, in which the fingerprints of individuals or the like are registered in advance instead of ID cards, and are collated at the time of entrance to the room.
In such an individual recognition system, an unauthorized person may pass a check by creating a replica of a registered fingerprint. For this reason, an individual recognition system needs to recognize whether an object is a living body, as well as performing fingerprint collation.
Conventionally, as a biometric recognition technique of detecting whether an object is a living body, a technique like that shown in FIG. 45 which uses impedance matching with an object has been proposed (see, for example, Japanese Patent Laid-Open No. 2000-172833). This biometric detection apparatus comprises an oscillation unit 73 which outputs a high-frequency signal, an electrode unit 70 of a non-resonant circuit formed from an electrode 71 to which the high-frequency signal from the oscillation unit 73 is applied and with which an object makes contact, a detection unit 74 which outputs a reflected wave signal corresponding to a change in the impedance of the electrode unit 70, a determination unit 76 which compares the reflected wave signal from the detection unit 74 with a predetermined reference signal to determine whether or not the object which contacts the electrode 71 is a living body, and a reference signal setting unit 75 in which a reference signal for determination whether or not the object is a living body is set in advance and which supplies the reference signal to the determination unit 76.
In this biometric detection apparatus, the oscillation unit 73 supplies a high-frequency signal to the electrode unit 70. The object is a living body such as a finger, and the impedance of the electrode unit 70 changes when the object contacts the electrode 71. Assume that when a human body contacts the electrode unit 70, the impedance of the object side matches the impedance on the input side of the electrode unit 70. In this case, if an object is a human body, the reflected wave of a high-frequency signal decreases due to the above impedance matching. The detection unit 74 detects this reflected wave. The determination unit 76 then compares it with the reference signal. If the reflected wave is lower than the detection level, it is determined that a human body has contacted the electrode unit.